1. Field of the Invention
This invention relates to a method and apparatus for handling system service requests in a multiprocessor environment and, in particular, to a method and apparatus for handling disk change requests in a device control unit having a plurality of concurrent communication adapters for attachment to host processors.
2. Description of the Prior Art
Communications and device controllers are, to an increasing extent, being implemented with multiple processors--more particularly, with multiple microprocessors. Typically, the implementation is done with a predefined function split, with the supplemental processors serving to handle low-level hardware interfaces and to provide a function-specific interface with the primary processor.
As a particular example, the IBM 3174 Subsystem Control Unit, which interconnects devices such as display terminals or printers to local or remote host processors, has a primary processor, which exercises general supervisory control over the operation of the control unit, as well as a plurality of host adapters, each of which contains a secondary processor for performing functions specific to that adapter. In addition to the usual communications between the primary processor and the secondary processor incident to the operation of the control unit to interface between the host processors and the devices, there are also those communications relating to such "housekeeping" operations as the handling of disk change requests or other system service requests.
It would be desirable if such requests could be made by an application running on a secondary processor without altering the application making the request.